Scanning probe microscopy system for and method of mapping nanostructures on the surface of a sample

Abstract

The present document relates to a scanning probe microscopy system and method for mapping nanostructures on the surface of a sample. The system comprises a sample support structure, a scan head including a probe comprising a cantilever and a probe tip, and an actuator for scanning the probe tip relative to the sample surface. The system also includes an optical source, and a sensor unit for obtaining a sensor signal indicative of a position of the probe tip. The sensor unit includes a partially reflecting element for reflecting a reference fraction and for transmitting a sensing fraction of the optical signal. It further includes directional optics for directing the sensing fraction as an optical beam towards the probe tip, and for receiving a reflected fraction thereof to provide a sensed signal. Moreover the sensor includes an interferometer for providing one or more output signals, and signal conveyance optics for conveying the sensed signal and the reference signal to the interferometer. The directional optics is configured for directing the sensing fraction such that at least a part of the sensing fraction is reflected by the probe tip such as to form the reflected fraction.

The invention claimed is: 
     
       1. A scanning probe microscopy system for mapping nanostructures on the surface of a sample, comprising:
 a sample support structure for supporting the sample, 
 a scan head including a probe comprising a cantilever and a probe tip arranged on the cantilever, 
 an actuator for scanning the probe tip relative to the sample surface for mapping of the nanostructures, 
 an optical source for providing an optical signal, and 
 a sensor unit for obtaining a sensor signal indicative of a position of the probe tip during scanning, the sensor unit comprising a sensor head that is a single element including:
 a partially reflecting element, configured to:
 reflect a reference fraction of the optical signal to provide a reference signal, and 
 transmit a sensing fraction of the optical signal; and 
 
 a directional optics configured for:
 directing the sensing fraction as an optical beam towards the probe tip, and 
 receiving a reflected fraction of the optical beam to provide a sensed signal, such that at least a part of the sensing fraction is reflected by the probe tip to form the reflected fraction; 
 
 
 wherein the system further comprises:
 an interferometer for enabling the sensed signal to interfere with the reference signal to provide one or more output signals via one or more outputs; and 
 a signal conveyance optics for conveying the sensed signal and the reference signal to the interferometer. 
 
 
     
     
       2. The scanning probe microscopy system in accordance with  claim 1 , wherein the directional optics is arranged for providing the optical beam such that the beam, near the probe tip, has a cross sectional beam area of a size sufficient to cover an operational range of positions of the probe tip during said scanning, such that at each position assumed by the probe tip, the reflected fraction returned by the probe tip is a non-zero fraction. 
     
     
       3. The scanning probe microscopy system according to  claim 1 , wherein the system further comprises at least one of the group consisting of:
 a low pass filter for filtering at least one of the output signals to filter signal components having a frequency above a first filter frequency; and 
 a high pass filter for filtering at least one of the output signals to filter signal components having a frequency below a second filter frequency. 
 
     
     
       4. The scanning probe microscopy system according to  claim 3 , wherein at least one of the first or the second filter frequency is within a range of 50 hertz to 10 kilohertz. 
     
     
       5. The scanning probe microscopy system according to  claim 3 , wherein at least one of the first or the second filter frequency is within a range of 500 hertz to 5 kilohertz. 
     
     
       6. The scanning probe microscopy system according to  claim 3 , wherein at least one of the first or the second filter frequency is at or around 2 kilohertz. 
     
     
       7. The scanning probe microscopy system according to  claim 1 , wherein the signal conveyance optics is arranged for conveying the reference signal and the sensed signal as a mixed signal to the interferometer, and
 wherein the signal conveyance optics comprises: 
 one or more splitting elements for splitting the mixed signal in a plurality of further mixed signals; and 
 one or more optical elements for establishing an optical path difference between two or more of the further mixed signals. 
 
     
     
       8. The scanning probe microscopy system according to  claim 7 , wherein the one or more optical elements of the signal conveyance optics are provided by at least a first and second optical branch path, configured to transmit one or more of the further mixed signals, wherein the first optical branch path has a different optical path length than the second optical branch path. 
     
     
       9. The scanning probe microscopy system according to  claim 1 , wherein the interferometer comprises an N-way coupler,
 wherein N is at least three, 
 wherein the N-way coupler comprises a first side with N first terminals and a second side with N second terminals, 
 wherein each one of the N first terminals is connected to one of the N second terminals by an optical conveyor, the optical conveyor being optically coupled for mutually exchanging optical signals conveyed by each conveyor, 
 wherein each one of at least two of the second terminals on the second side is connected to an optical fiber path of a unique optical path length to establish an optical path difference between the optical signals provided through said at least two of the second terminals, and 
 wherein the optical elements further comprises a reflector element for returning an output signal through the first terminals at the first side, the first terminals thereby providing the one or more outputs of the interferometer. 
 
     
     
       10. The scanning probe microscopy system according to  claim 1 , wherein the one or more outputs of the interferometer are connected to a signal processor,
 wherein the signal processor comprises one or more light intensity detectors optically coupled to the one or more outputs of the interferometer, and 
 wherein a signal processing circuit is coupled to the light intensity detectors and configured to determine information representing a distance traveled by the sensed signal from the partially reflective element via the directional optics and the optical beam to the probe tip and back, to measure a motion of the probe tip during said scanning. 
 
     
     
       11. The scanning probe microscopy system according to  claim 1 , wherein the scan head includes at least the optical source and the sensor unit, including the partially reflecting element, the directional optics, and the signal conveyance optics. 
     
     
       12. The scanning probe microscopy system according to  claim 1 , the scanning probe microscopy system being configured for performing one or more functions taken from the group consisting of:
 atomic force microscopy, 
 ultrasonic force microscopy, 
 heterodyne ultrasonic force microscopy, 
 near-field microscopy, 
 optical microscopy, 
 nanometer scale manipulation, and 
 micrometer scale manipulation. 
 
     
     
       13. A method of performing scanning probe microscopy using a scanning probe microscopy system that comprises a sample support structure for supporting the sample, a scan head including a probe comprising a cantilever and a probe tip arranged on the cantilever, an actuator for scanning the probe tip relative to the sample surface for mapping of the nanostructures, an optical source for providing an optical signal, and a sensor unit for obtaining a sensor signal indicative of a position of the probe tip during scanning, wherein the sensor unit comprising a sensor head that is a single element that comprises:
 a partially reflecting element, configured to:
 reflect a reference fraction of the optical signal to provide a reference signal, and 
 transmit a sensing fraction of the optical signal; 
 
 a directional optics configured for:
 directing the sensing fraction as an optical beam towards the probe tip, and 
 receiving a reflected fraction of the optical beam to provide a sensed signal, such that at least a part of the sensing fraction is reflected by the probe tip to form the reflected fraction; 
 
 wherein the system further comprises:
 an interferometer for enabling the sensed signal to interfere with the reference signal to provide one or more output signals via one or more outputs, and 
 a signal conveyance optics for conveying the sensed signal and the reference signal to the interferometer, and 
 
 wherein the method comprises:
 reflecting, using the partially reflecting element, the reference fraction of the optical signal to provide the reference signal; 
 transmitting, using the partially reflecting element, the sensing fraction of the optical signal; 
 directing, using the directional optics, the sensing fraction as the optical beam towards the probe tip, and receiving with the directional optics the reflected fraction of the optical beam to provide the sensed signal, such that at least a part of the sensing fraction is reflected by the probe tip to form the reflected fraction; 
 conveying, using the signal conveyance optics, the sensed signal and the reference signal to the interferometer; and 
 interfering, using the interferometer, the sensed signal with the reference signal to provide one or more output signals provided via one or more outputs. 
 
 
     
     
       14. The method according to  claim 13 , wherein directing the sensing fraction as an optical beams towards the probe tip comprises:
 providing the optical beam such that the beam, near the probe tip, has a cross sectional beam area of a size sufficient to cover an operational range of positions of the probe tip during said scanning, such that at each position assumed by the probe tip, the reflected fraction returned by the probe tip is a non-zero fraction. 
 
     
     
       15. The method according to  claim 13 , further comprising analyzing at least one of the output signals provided via the one or more outputs for determining a distance traveled by the sensed signal from the partially reflective element via the directional optics and the optical beam to the probe tip and back, such as to measure a motion of the probe tip during said scanning. 
     
     
       16. The method according to  claim 15 , wherein the step of analyzing comprises:
 analyzing the at least one output signal in a first frequency range for measuring a first displacement signal indicative of probe motion of the whole probe; and 
 analyzing the at least one output signal in a second frequency range for measuring a second displacement signal indicative of probe tip motion of the probe tip relative to the scan head; 
 wherein the first frequency range includes lower frequency values than the second frequency range. 
 
     
     
       17. The method according to  claim 13 , wherein the reference signal and the sensed signal are conveyed as a mixed signal to the interferometer, and wherein the method comprises splitting the mixed signal, by at least one of the signal conveyance optics and the interferometer, in a plurality of further mixed signals and establishing an optical path difference between two or more of the further mixed signals.